The present invention is a process for redistributing an alkyl-rich silalkylene-containing residue. The process comprises contacting an alkyl-rich silalkylene-containing residue with a halosilane selected from the group consisting of alkyltrihalosilanes and tetrahalosilanes in the presence of an effective amount of a redistribution catalyst thereby forming a redistribution product comprising dialkyldihalosilane. At least a portion of the catalyst required for conducting the process may be formed in situ during direct process operation and isolation of the residue.
Alkylhalosilanes prepared by the direct process form a complex mixture which is typically distilled to separate methylchlorosilanes from other components present in the mixture. After the methylchlorosilanes are distilled from the mixture, remaining are monosilane, disilane and silalkylene by-product fractions. The disilane and silalkylene fractions which boil above about 80.degree. C. are hereinafter referred to as "alkyl-rich silalkylene-containing residues." In current commercial operations for performing the direct process, the alkyl-rich silalkylene-containing residues alone can constitute as much as five weight percent of the resultant product. Therefore, it is desirable to treat the alkyl-rich silalkylene-containing residues to produce commercially desirable products to reduce by-product disposal and to improve raw material utilization.
The "direct process" is well described in the patent literature, for example, in Rochow, U.S. Pat. No. 2,380,995 and Barry et al., U.S. Pat. No. 2,488,487. The high-boiling fraction remaining after the monosilanes overhead distillation is a complex mixture comprising higher boiling silicon containing compounds which have, for example, SiSi, SiOSi, and SiCSi linkages in the molecules. The high-boiling fraction may also contain particulate silicon and metals or compounds thereof. Typical high-boiling fractions obtained from the direct process distillation product are described, for example, in Mohler et al., U.S. Pat. No. 2,598,435 and Barry et al., U.S. Pat. No. 2,681,355.
Wagner, U.S. Pat. No. 2,606,811, teaches a hydrogenation process where a compound containing a halogen and the Si-Si bond is heated to at least 300.degree. C. in the presence of hydrogen. The resultant products are monosilanes.
Atwell et al., U.S. Pat. No. 3,639,105, describe a process where hydrosilanes are produced by contacting a disilane with hydrogen gas under pressure and heating the mixture in the presence of a transition metal catalyst such as palladium on charcoal. Atwell et al. state that the disilane may be part of a mixture from the direct process. Atwell et al. further report that when the disilane was a methylchlorodisilane, the resulting product contained about four to 28 weight percent methyltrichlorosilane. Generally, organotrihalosilanes such as methyltrichlorosilane have limited commercial usefulness and for this reason limit the usefulness of the process described by Atwell et al.
Neale, U.S. Pat. No. 4,079,071, describes a process for preparing hydrosilanes in high yields by reacting methylchloropolysilanes with hydrogen gas under pressure at a temperature from 25.degree. C. to about 350.degree. C. in the presence of a copper catalyst. Neale states that the methylchloropolysilanes can be those typically created as direct process by-products. Useful catalysts described by Neale include copper metal, copper salts, and complexes of copper salts with organic ligands. In some cases, Neale reports that up to 29 weight percent methyltrichlorosilane was formed.
Ritzer et al., U.S. Pat. No. 4,393,229, describe a process for converting alkyl-rich disilanes in residue obtained from the manufacture of alkylhalosilanes to halogen-rich polysilanes. The process comprises treating an alkyl-rich disilane-containing residue with an alkyltrihalosilane or silicon tetrahalide in the presence of a catalyst and a catalytic amount of a hydrosilane reaction promoter at an elevated temperature. Ritzer et al. teach aluminum trichloride as a useful catalyst in the process when used with a hydrosilane promoter. Ritzer et al. further teach that the resulting halogen-rich polysilanes can, in a separate step, be cleaved to form monosilanes.
Bokerman et al., U.S. Pat. No. 5,175,329, describe a process for the producing organosilanes from the high-boiling residue resulting from the direct process that results in a net consumption of organotrichlorosilane. In the process, the high-boiling residue is contacted with an organotrichlorosilane and hydrogen gas in the presence of a hydrogenation catalyst and a redistribution catalyst.
Ferguson et al., U.S. Pat. No. 5,430,168, describe a process for producing monosilanes from the high-boiling residue resulting from the "direct process." The process comprises forming a mixture comprising an organotrihalosilane and high-boiling residue in the presence of hydrogen gas and a catalytic amount of aluminum trichloride. The process results in organotrihalosilane consumption and conversion of the high-boiling residue to useful monosilanes.
The present invention provides a process for redistributing alkyl-rich silalkylene-containing residues resulting from the direct process for producing methylchlorosilanes. The present inventor has discovered that by contacting the alkyl-rich silalkylene containing residue with a halosilane selected from the group consisting of alkyltrihalosilanes and tetrahalosilanes in the presence of an effective amount of a redistribution catalyst that a redistribution product is produced containing halogen-rich silalkylenes and more valuable dialkyldihalosilanes. The present invention provides a process for improving the utilization of valuable alkyl groups from alkyl-rich silalkylene-containing residue obtained form the production of methylchlorosilanes while simultaneously converting the halosilanes to commercially more valuable dialkyldihalosilanes. At least a portion of the catalyst required for conducting the process may be formed in situ during the direct process operation and isolation of the residue.